The present invention relates to scanning electron microscopes and more particularly, to a scanning electron microscope which performs autofocus adjustment on a plurality of types of images having different features.
For increasing the yield of semiconductor devices, an inspection step is indispensable. For increasing a production efficiency by locating a cause of yield reduction, an electron microscope for inspecting and identifying an abnormality in a wafer is indispensable. For efficient inspection, it is indispensable to speed up the inspection and thus it is desirable to inspect a number of points in a short time.
One of the elements to be considered for the inspection speed-up is an autofocus adjustment function of adjusting the focus of an image in an electron microscope, which function is indispensable for picking up a clear image. One of such functions is disclosed, for example, in JP-A-2005-332593 as a method of achieving accurate autofocus. In the autofocus adjustment function disclosed in JP-A-2005-332593, a plurality of images are acquired by changing a focus, high frequency responses for these images are calculated, and a focus position corresponding to biggest one of the responses is calculated for automatic focus adjustment.